Revised end of Lecture 2: Effective Mass Yield - EMY Imperial College London mass of desired product EMY = x 100 % mass of non-benign reagents Whereas atom economies and E-factors are unlikely to measure the true sustainability of a chemical reaction, EMY values do discriminate between environmentally benign and non-benign reagents. 4.I6 2 - A1

EMY indicates that the reaction is very 'green' Green Metrics - the corrected slide from lecture 2 Imperial College London e.g. esterification of n-butanol with acetic acid Typical procedure: 37g butanol, 60 g glacial acetic acid and 3 drops of H2SO4 are mixed together. The reaction mixture is then poured into 250 cm3 water. The organic layer is separated and washed again with water (100 cm3), saturated NaHCO3 (25 cm3) and more water (25 cm3). The crude ester is then dried over anhydrous Na2SO4 (5 g), and then distilled. Yield = 40 g (69 %). Metric Value Greenness yield 69 % Moderate atom economy 85 % Good (byproduct is water) E-factor 462 / 40 = 12.2 Poor EMY 40/37 x 100 = 108 % Very good EMY indicates that the reaction is very 'green' 4.I6 2 - A2

Remember Lecture 1 - "Green Chemistry is not easy!" Recap of the conclusions from lecture 2 Imperial College London Atom efficiencies and E-factors are often useful, simple guides to the 'greenness' of reactions, but may be overly focussed on waste. EMY values take into account the toxicity of reagents and are therefore more likely to reflect the true 'greenness' of a process. However, EMY values require us to decide what and what is not benign! The only true way of judging 'greenness' is by a life cycle analysis, but this is far too time consuming to be practical. We therefore use atom economies, E-factors and EMY data as simple (but imperfect) guides. Remember Lecture 1 - "Green Chemistry is not easy!" The difficulties measuring greenness are a major reason. 4.I6 2 - A3

Exam style question - answer next time Imperial College London Maleic anhydride may be prepared using two routes: Oxidation of benzene: Oxidation of but-1-ene: The benzene oxidation route typically occurs in 65 % yield, while the but-1-ene route only gives yields of 55 %. (a) Assuming that each reaction is performed in the gas phase only, and that no additional chemicals are required, calculate (i) the atom economy and (ii) the effective mass yield of both reactions. You should assume that O2, CO2 and H2O are not toxic. (b) Which route would you recommend to industry? Outline the factors which might influence your decision. 4.I6 2 - A4

Lecture 3: Renewable versus Depleting Resources 4.I6 Green Chemistry Imperial College London Lecture 3: Renewable versus Depleting Resources or Biomass versus Petrochemicals "Many of the raw materials of industry…can be obtained from annual crops grown on the farms" Henry Ford, 1932 4.I6 Green Chemistry Lecture 3 Slide 1

Lecture 3 - Learning Outcomes Imperial College London By the end of this lecture you should be able to describe the concept of carbon neutrality describe the use of biomass as a source of renewable fuels explain how biomass may be used as a source of chemicals 4.I6 3 - 2

Major petrochemical building blocks Imperial College London Seven major raw materials from petroleum: C2-C4 and BTX ethylene propylene butenes butadienes benzene (B) toluene (T) xylenes (X) Each also has extensive derivative chemistry, e.g. ethylene CH2=CH2 Cl2 H2, CO O2 , H2O, PdCl2 C6H6 CH2ClCH2Cl CH3CH2CHO O2, Ag CH3CHO PhCH2CH3 -HCl O2 O2, AcOH, PdCl2 O2 CH2=CHCl -H2 CH3CH2CO2H H2 O2 H2O H2O CH3CO2H CH2=CHPh CH2=CHOAc CH3CH2CH2OH HOCH2CH2OH (CH3CO)2O CH3CH2OH 4.I6 3 - 3

The problem with petroleum? Its use as a fuel… Imperial College London non-sustainable adverse direct and indirect environmental effects limited supplies (economic pressure and potential security risk) political entanglement Definition of sustainable development: "meeting the needs of the present without compromising the ability of future generations to meet their own needs" UN Bruntland Commission 1987 But the vast majority of contemporary industrial chemistry is based on petrochemicals - in the US > 98 % of all commercial chemicals are derived from petroleum (in Europe it is > 90 %) 4.I6 3 - 4

biomass + other renewables Energy consumption Imperial College London oil gas coal biomass + other renewables nuclear hydro Projected Global Energy Consumption to 2030 1971 1980 1990 2000 2010 2020 2030 5 10 15 109 tonnes of oil equivalent energy demands will increase and so will CO2 production biomass-based fuels attracting increasing attention Source: World Energy Outlook 2005 (International Energy Authority) 4.I6 3 - 5

Cellulose - Sugars / Starches What is biomass? Imperial College London Biomass is all organic (living and dead) material on the planet. More realistically, the biomass that we shall consider in this lecture is made up of: agricultural residues food processing wastes livestock production wastes municipal solid waste wood waste Chemical composition Cellulose - Sugars / Starches Hemicellulose Lignin 4.I6 3 - 6

But doesn't burning biomass still produce CO2? Imperial College London (CH2O)n + n O2 n CO2 + n H2O Biomass is said to be carbon neutral, i.e. the CO2 absorbed from the atmosphere during plant growth is returned to it upon burning. biomass oil natural gas Energy release on 15 45 55 combustion (GJ tonne-1) As burning biomass is less calorific than burning fossil fuels, alternative ways to produce energy from it have attracted attention. What is the difference between carbon neutrality and carbon offsetting? 4.I6 3 - 7

Energy from biomass Imperial College London Method employed depends on the source of biomass (and on its water content) 15 % combustion thermolysis (450 - 800 °C) pyrolysis (1500 °C) gasification (650 - 1200 °C) hydrothermolysis (250 - 600 °C) fermentation anaerobic digestion heat, CO2, H2O charcoal, fuel, gases So will using biomass for energy increase the supply of renewable feedstocks? C2H2, charcoal CO, H2, CH4, CO2 water content biorenewable raw materials? charcoal, fuel, CO2 ethanol, CO2 > 85 % CH4, H2O 4.I6 3 - 8

component of vegetable oil Biofuels - 1. Biodiesel Imperial College London Production of Biodiesel fatty acid ester, biodiesel triglyceride, main component of vegetable oil e.g. palm oil based triglycerides contain: 42.8 % palmitic acid (1-hexadecanoic acid; CH3(CH2)14CO2H) 40.5 % oleic acid (cis-9-octadecenoic acid; CH3(CH2)7CH=CH(CH2)7CO2H) 10.1 % linoleic acid (cis,cis-9,12-octadecadienoic acid; CH3(CH2)3(CH2CH=CH)2(CH2)7CO2H) 4.5 % stearic acid (1-octadecanoic acid; CH3(CH2)14CO2H) 0.2 % linolenic acid (cis,cis,cis-9,12,15-octadecatrienoic acid; CH3(CH2CH=CH)3(CH2)7CO2H) Other sources include soybean, rapeseed and sunflower seed. 4.I6 3 - 10

Biodiesel: pros and cons Imperial College London Advantages: GM can increase oil yield (some sunflower seeds contain 92% oleic acid) Bacteria could be even more productive Wide range of oils tolerated (even waste chip-shop oil can be recycled in this way) Carbon neutral fuel source (in theory) and biodegradable Glycerin by-product Disadvantages: Land use (maximum biodiesel fraction of car fuel market in the UK ≈ 5 %) Higher viscosity than normal diesel (unreliable in cold weather) To keep costs low the transesterification step must be fast - catalyst is often NaOH which also causes saponification (ester hydrolysed to Na salt of fatty acid), which necessitates lengthy separation procedures. 4.I6 3 - 11

Metal carboxylates Sulfosuccinates Alcohol ethoxylate But fatty acids may also be used as chemical raw materials Imperial College London 1. Modification of the acid function Wax esters (lipids) Metal carboxylates triglyceride Fatty amides ROH NR3 -H2O Na, Al, Zn, Mg hydroxides Fatty acid Nitriles H2 H2 1-alkenes -H2O Fatty alcohol Amine ethylene oxide RX Sulfosuccinates (surfactants) R4N+ salts Alcohol ethoxylate (pesticides) Na2SO3 maleic anhydride 4.I6 3 - 12

Fatty acids chemistry continued Imperial College London 2. Modification of the alkene function medium chain acids and alkenes short chain acids and diacids olefin metathesis (C2H4) ozonolysis conjugated fatty acids (lipids) base H+ or NOx Fatty acid cis-trans isomers (i) H+, H2O (ii) H2 [O] diols (precursors for polyurethanes) epoxides 4.I6 3 - 13

(PVC antiblocking agent) Example: erucic acid (C22) Imperial College London brassylic acid (nylon 13,13 precursor and musks) erucamide (slip agent) HO2C(CH2)11CO2H erucic acid (rapeseed) CH3(CH2)20CO2H CH3(CH2)20CH2OH behenic acid (PVC antiblocking agent) behenyl alcohol (cosmetics) 4.I6 3 - 14

Large amount of research now looking at the Biofuels - 2. Bioethanol Imperial College London yeast C6H12O6 2 C2H5OH + 2 CO2 Advantages Cheap hydrated bioethanol can be used neat as a car fuel, but requires specially adapted engines. Anhydrous bioethanol must be mixed with petrol (up to 22 %) but can then be used in conventional engines. Disadvantages Of all the saccharides present in biomass, only glucose is readily fermented, lowering competitiveness and increasing waste (genetic engineering may solve this problem). Enzymes do not operate if the EtOH concentration is too high (typically needs to be < 15 %). Energy intensive and expensive distillation is therefore required. Large amount of research now looking at the conversion of ligninocellulosic feedstocks into sugars 4.I6 3 - 15

12 major sugar derived chemicals Imperial College London 1,4-diacids, e.g succinic acid 2,5-furandicarboxylic acid 3-hydroxypropionic acid aspartic acid glucaric acid glutamic acid itaconic acid levulinic acid 3-hydroxybutyrolactone glycerol sorbitol xylitol 4.I6 3 - 16

Each has extensive derivative chemistry, e.g. levulinic acid Imperial College London c-valerolactone cellulose 2-methyl THF solvent, fuel oxygenate solvent H2SO4 > 200°C acrylic acid glucose 1,4-pentanediol monomer 200°C polyester precursor 5-amino levulinic acid levulinate esters -HCO2H herbicide biodiesel additive diphenolic acid acetyl acrylic acid monomer levulinic acid bisphenol A substitute 4.I6 3 - 17

The difference between petrochemicals and biomass chemicals? Imperial College London Slide 3 Slide 17 Hydrocarbon-based chemistry Carbohydrate-based chemistry The major difference is oxygen content 4.I6 3 - 18

toluene steam dealkylation An alternative source of biomass chemicals - Syn-gas Imperial College London Three classical routes: Steam reforming of methane Shell Gasification process Coal gasification 1 : 3 1 : 1 1 : 1 1 : 0 In theory any hydrocarbon can be used, e.g. toluene steam dealkylation 4.I6 3 - 19

Existing Syn-gas technology Imperial College London polyethylene aldehydes acids alcohols CO, H2 -H2O esters ethers oligomers C2H4 EtOH O2 + Ag ethylene oxide Biomass CO + H2 H2O + Rh catalyst N2 Fischer Tropsch NH3 Gasoline CO2 CO + Ir / Rh cat. CH3CO2H HCHO urea MeOH zeolite H-ZSM-5 alkanes ROH CO, H2 HCl Al2O3 / Pt urea-formaldehyde (Bakelite) resins acrylic acid aromatics polymers MeCl 4.I6 3 - 20

Renewable chemical feedstocks - summary Imperial College London Four approaches: use naturally-occurring chemicals extracted directly from plants e.g. natural rubber, sucrose, vegetable oils, fatty acids, starch use chemicals extracted by a one-step modification of biomass e.g. fermentation to give lactic acid (lecture 2), bioethanol, furans, levulinic acid, adipic acid, poly(hydroxyalkanoates) synthesise chemicals by multi-step conversion of biomass chemicals e.g. polylactide use biomass as a source of basic building blocks (H2, CO, CH4 etc) e.g. Syn-gas economy, polyethylene The four approaches will now be exemplified using examples from polymer chemistry. 4.I6 3 - 9

Renewable polymers - approach 1 Imperial College London The four approaches to using biomass-derived feedstocks are all found in polymer chemistry. Approach 1: use naturally-occurring chemicals extracted directly from plants e.g. starch amylopectin amylose Advantages of polysaccharides Cheap and biodegradable Disadvantages Crystalline (not plastic) Properties difficult to modify e.g. cellulose 4.I6 3 - 21

Accumulation of PHA in rhodobacter sphaeroides Approach 2: one-step modification of biomass Imperial College London e.g. Polyhydroxyalkanoates - PHAs R = Me: poly(hydroxybutyrate) - PHB R = Et: poly(hydroxyvalerate) - PHV In the absence of N2 bacteria form PHAs as energy storage (just as plants produce starch). Accumulation of PHA in rhodobacter sphaeroides Advantages of PHAs: Desirable physical properties (PHB is similar to polypropylene) and biodegradable Disadvantages: High cost of production and processing ($15 per kg - polyethylene costs $1 per kg) 4.I6 3 - 22

polylactic acid, PLA lactide oligomers Approach 3: multi-step conversion of biomass chemicals Imperial College London e.g. Poly(lactic acid) - PLA enzymatic degradation fermentation corn starch lactic acid step-growth condensation (-H2O) ring-opening polymerisation heat (chain growth) polylactic acid, PLA lactide oligomers 4.I6 3 - 23

in a distinctly green manner… Polylactide Imperial College London The synthesis of PLA is now being carried out on an industrial scale by Cargill in a distinctly green manner… 160 °C No solvent - reaction is a melt phase polymerisation The industrial process is 'catalysed' by tin (II) bis(2-ethylhexanoate). The development of other catalysts for this process is dealt with in 4I-11: 3pm Friday 2nd and Friday 9th March 4.I6 3 - 24

ethylene oxide urea-formaldehyde (Bakelite) resins acrylic acid Approach 4: The Syn-gas economy Imperial College London polyethylene aldehydes acids alcohols CO, H2 -H2O esters ethers oligomers C2H4 EtOH O2 + Ag monomers ethylene oxide Biomass CO + H2 H2O + Rh catalyst polymers N2 Fischer Tropsch NH3 Gasoline CO2 CO + Ir / Rh cat. CH3CO2H HCHO urea MeOH zeolite H-ZSM-5 alkanes ROH CO, H2 HCl Al2O3 / Pt urea-formaldehyde (Bakelite) resins acrylic acid aromatics polymers MeCl 4.I6 3 - 25

Four ways biomass can be used to provide raw materials: Conclusions Imperial College London Although entirely different, global warming and green chemistry share a common potential solution - biomass. Biomass can be converted into fuel and into raw materials for the chemical industry in the same way that oil is currently used to produce fuel (petroleum) and petrochemicals (particularly C2 - C4 alkenes, and BTX aromatics). Four ways biomass can be used to provide raw materials: (i) direct use of naturally occurring compounds (ii) one step modification of biomass (iii) multi-step conversion of biomass (iv) gasification of biomass to syn-gas The use of biomass as a source of fuel fits well into existing petrochemical infrastructure. The use of biomass as a source of raw materials requires the development of new reduction chemistry (petrochemicals use oxidation chemistry). 4.I6 3 - 26

Learning outcomes revisited Imperial College London By the end of this lecture you should be able to explain the concept of carbon neutrality describe the use of biomass as a source of renewable fuels describe the use of biomass as a source of chemicals Burning biomass returns CO2 to the atmosphere. Burning fossil fuels increases atmospheric CO2. Low temperature: biotechnology / fermentation to produce bioethanol. High temperature: charcoal, gases, heat etc. Fatty acids: production of biodiesel. Potentially most important: gasification to syn-gas and subsequent Fischer-Tropsch like chemistry 4.I6 3 - 27